This invention relates to a method for producing polymers; more particularly, to a method for producing carborane-siloxane polymers directly from a salt of the corresponding carborane.
Carborane-siloxane polymers are known to have excellent high temperature characteristics and to be useful in applications such as gaskets, seals, wire and cable insulation and the like where high temperature properties are desired. These polymers may be represented by a recurring unit of the following formula (I): ##STR1## wherein R.sup.1 and R.sup.2, which may be the same or different, each represents hydrogen or a group containing up to 14 carbon atoms and selected from the group consisting of alkyl, alkenyl, cycloalkyl, aryl, alkaryl, aralkyl, alkoxyaryl, haloalkyl, haloaryl, cyanoalkyl, and pyridinyl; R.sup.4 and R.sup.5, which may be the same or different, each represents hydrogen or a group containing up to 14 carbon atoms and selected from the group consisting of alkyl, alkenyl, aryl, alkaryl, alkoxyaryl, alkoxyalkyl, haloalkyl, haloaryl and cyanoalkyl; X represents a divalent radical derived from a carborane which may be 1,7-decacarborane, 1,10-octacarborane, 1,6-octacarborane, 2,4-pentacarborane, 1,6-tetracarborane, 9-alkyl-1,7-decacarborane, 9,10-dialkyl-1,7-decacarborane, 2-alkyl-1,10-octacarborane, 8-alkyl-1,6-octacarborane, decachloro-1,7-decacarborane, octachloro-1,10-octacarborane, decafluoro-1,7-decacarborane, octafluoro-1,10-octacarborane, or mixtures thereof; and m and n individually have a value of from 0 to 4. The molecular weight of the polymers is not critical and may vary over a wide range depending on the properties desired. Generally, the elastomeric properties of these polymers improve with increasing molecular weight; however, their processability decreases at the same time. Therefore, depending on the properties and processability desired those skilled in the art will realize that polymers of varied molecular weight are possible. For example, the weight average molecular weight may vary from 5,000 to 150,000, and higher.
Commonly-assigned, U.S. Pat. No. 4,145,504 which issue Mar. 20, 1979, discloses several methods for the preparation of linear, high molecular weight polymers of the type of formula (I). Specifically, as taught therein, linear carborane-siloxane polymers may be formed by the condensation of silyl diamines or .alpha..omega.-diaminosiloxanes with carborane disilanols. In a second embodiment, such linear polymers are also prepared by the condensation of bis-ureido-silanes or .alpha.2/3-bis-ureido-siloxanes with carborane disilanols. In a further embodiment, carborane disilanols can be condensed with silyl bis-carbamates or .alpha..omega.-carbamoylsiloxanes to form such carborane-siloxane polymers. Illustrative of all of the R groups as hereinbefore de defined are such groups as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-butenyl, n-hexenyl, cyclopentyl, cyclohexyl, phenyl, benzyl, o-,m-, or p-chlorophenyl, o-,m- or p-methylphenyl, o-,m-, or p-methoxyphenyl, 3,3,3-trifluoropropyl, cyanomethyl, morpholinyl, pyridinyl and the like. The R groups need not be the same in any one polymeric chain. Particularly preferred are groups containing up to 7 carbon atoms. The carborane disilanols employed in these processes represented by formula (III), may be prepared as shown in equations (1)-(3): ##STR2## wherein X, R.sup.4 and R.sup.5 are as previously indicated.
The preparation of the carborane disilanol (III) is expensive and time-consuming, as is, to a lesser extent, the preparation of the bis-ureido-silanes and bis-ureido-siloxanes, and other monomers employed in the synthesis of these polymers. The novel method of the invention eliminates these disadvantages and enables one to prepare carborane-siloxane polymers employing materials which are all commercially available and/or readily accessible.
In U.S. Pat. No. 3,397,221 there is disclosed a process for the preparation of organosiloxane-containing carborane monomers which are prepared via a dialkyl metal derivative of carborane and a dihalogen organosiloxane in a stoichiometric-ratio of 2 to 1 or greater. The monomers after separation and purification can then be reacted with dialkoxy silanes in the presence of ferric chloride to form linear polymeric products. In contrast, the process of this invention provides a direct route to the desired polymers without the need for preparing an isolating organosiloxane-containing carborane monomers.